Both Windows and Linux builds of Project Zomboid should now include its own, internal, version of either the OpenJDK (Linux) or Oracle's JRE (Windows). The only exception is on Macs, but these systems require you to use the version of Java provided by Apple.

There is no (simple) way to bypass this.

Installing or updating Java is thus a futile endeavour. If you have technical issues, they'll likely result from one of two things, now that Steam can be eliminated from the problem domain: OpenGL support and your video adapter drivers (Pixel Format not Accelerated) and Minecraft (Picked up _JAVA_OPTIONS: -Xmx512M). These errors should be visible from the console that launches with the game, or can be gleamed by going to %UserProfile%\Zomboid\ and opening Console.txt.

Having to install Java has been the reason I haven't played / purchased this game

I should add that since Java is bundled, it does not have the same security risks associated with installing Java that may concern potential customers. The JRE is only used by the Zomboid executable directly and not installed onto the OS.